The invention relates to a femur marrow nail for insertion between the condylii of a knee joint having an anchoring in the region of the nail tip, having a curvature provided in the sagittal plane and having a straight end piece which has fastening bores with axes B, C for its fastening.
Such femur marrow nails are used when an opening occurs in the knee joint. It frequently occurs in accidents that fragments are produced in the region of the condylii of the knee joint. The previous healing methods consist of plates attached to the femur bone with bone screws (Manual of osteosynthesis, Springer Verlag, 1992: FIGS. 12.10; 12.11; 12.12), which result in a large operation field or in marrow nails such as are shown in patent application EP-A-0 827 717.
In EP-A-0 827 717, a plurality of screw connections extending parallel to one another through a shank are shown, with their entrance apertures, and possibly their exit apertures, lying in the region of the actual joint and being able to have effects on ligaments, nerves and blood vessels and thus indirectly making the healing process more difficult. The invention is intended to counter this circumstance. It has the object of improving the fixing of fragments in the condylar region and achieves this by at least two fastening bores with axes B and C crossing the longitudinal axis X of the end piece at a spacing of less than 70 millimeters from the end of the end piece and penetrating with its axes B and C a plane which includes the end and is perpendicular to the longitudinal axis X at a spacing r from the X axis in a region 10 mmxe2x89xa6rxe2x89xa6116 mm in order to grip hard bone zones with fastening screws in the region of the condylii.
This arrangement has the advantage that an anchoring can be effected in the spreading direction and in hard bone layers, for example in posterior regions of the condylii, in the condylii which are spread apart from the longitudinal axis of the femur bone like the upper part of a xe2x80x9cYxe2x80x9d. A further advantage lies in the fact that only a minimum of bone openings is required in the direct region of the joint surfaces.
Advantageous further developments of the invention result from the dependent claims 2 to 12. The following number data for angles relate to a right knee. The system must be imagined in a mirror image for a left knee.
Particularly favourable arrangements result when, in a projection in the direction of the longitudinal axis X of the end piece, the axis B extends in an angle region of 35xc2x0xe2x89xa6xcex22xe2x89xa655xc2x0, and the axis C in an angle region 30xc2x0xe2x89xa6xcex23xe2x89xa645xc2x0, to the sagittal plane and when the axis B forms an angle of 110xc2x0xe2x89xa6xcex12xe2x89xa6150xc2x0, and the axis C an angle of 125 xc2x0xe2x89xa6xcex13xe2x89xa6160, xc2x0 with the longitudinal axis X. The associated bone screws can be inserted particularly far into the condylii in such an arrangement and support these without the joint surfaces and their direct environment being impaired.
If the longitudinal axis X is crossed perpendicular to the sagittal plane, when considered from the end of the marrow nail, by an axis A of a transverse verse bore at a spacing of 10 mmxe2x89xa6X1xe2x89xa618 mm, by the axis B at a spacing of 20 mmxe2x89xa6X2xe2x89xa642 mm, and by the axis C at a spacing of 30 mmxe2x89xa6X3xe2x89xa670 mm, the hard posterior bone regions can be reached for different condylus sizes.
A better guide length can be achieved for the bone screw with an end piece whose diameter is greater than that of the remaining marrow nail. At the same time, a larger radial support surface is produced for the end piece in the bone. The finding of the bores in the axes A, B and C is carried out by a target wire which is fastened in form-locking manner to the driven in marrow nail and which has bore guides in the direction of the axes A, B and C in order to bore the bone up to the bores in the marrow nail with a smaller diameter than that of the later bone screws. The bone screws can be self-tapping.
The marrow nail can be provided with a kink between the end piece and the actually longer part of the marrow nail. Such a kink allows the end piece to be made straight and within low tolerances in the region of the target wire and nevertheless to follow the curvature of the femur bone in the sagittal plane. The kink is kept smaller than 8xc2x0 in order to remain in the region of the curvature of the femur.
In accordance with a usual operation technique, the bone marrow can be hollow, that is cannulated, in order to be driven in along a guide wire. It can also have an elongate slit outside the end piece in order to achieve a greater elasticity.